The invention relates to utility vehicles for industrial and agricultural use, such as utility tractors. Particularly, the invention relates to transmission control systems for such vehicles.
Typical utility vehicles, such as compact tractors, utilize an engine operating substantially at a pre-selected speed that drives a transmission system or drive train that delivers power to one or more driven wheels. The transmission system includes a speed controllable transmission component, a gear selection component, and a differential component. The speed controllable transmission component can be, for example, a hydrostatic transmission, or a transmission that uses electro-hydraulically controlled forward and reverse clutch packs to initially accelerate the vehicle and to change vehicle direction (hereinafter referred to as a xe2x80x9creverser transmissionxe2x80x9d), such as a POWRREVERSER(trademark) transmission incorporated in JOHN DEERE Series 4000 tractors.
The present inventors have recognized that the desired xe2x80x9caggressivenessxe2x80x9d of a vehicle""s performance, or rates of acceleration and deceleration in response to operator commands, depends on operator experience, the operating conditions of the vehicle and the work being performed with the vehicle. For example, experienced operators performing material handling work tend to prefer a vehicle that accelerates and decelerates aggressively, and allows quick changes in direction. An operator that is using a vehicle for turf care work would prefer less aggressive accelerations and decelerations to prevent damage to the grass caused by slipping of the vehicle wheels.
For hydrostatic transmissions and reverser transmissions, pre-selecting the vehicle performance is commonly done by sizing orifices to control the rate of fluid flow to the servo control system of the hydrostatic transmission or control the rate of fluid flow to clutch packs in the reverser transmission. With electronically controlled systems, the aggressiveness is commonly controlled by pre-selecting the rate of increase of the electrical control current to electro-hydraulic pressure reducing valves that control swashplate servo systems or clutch pack hydraulic pressures.
However, compact utility tractors are commonly used for both material handling and turf care as well as many other operations. The present inventors have recognized the desirability of providing a utility tractor that would allow the driver to choose the aggressiveness of the tractor""s performance according to the work being done. Such a selectable aggressiveness would lead to improved tractor productivity.
The present invention provides for operator selection of vehicle xe2x80x9caggressiveness,xe2x80x9d or rates of acceleration in response to operator command. The aggressiveness of a vehicle""s performance can be controlled by modulating control signals to control valves, control valves which determine the acceleration of the vehicle transmission, according to two or more electrical ramp-up (or ramp-down) profiles, in response to an operator""s acceleration command (or deceleration command).
The selection of vehicle aggressiveness controls the acceleration rates of the vehicle in both forward and reverse operation.
According to the preferred embodiment of the present invention, a vehicle transmission control system includes a controller, directional switches or potentiometers and electro-hydraulic control valves which control hydraulic pressure in the clutch pack hydraulics in the reverser transmission.
The operator is provided with a two-position set switch. With the set switch in the less aggressive position, in response to an operator""s command, the software in the controller provides a relatively slow current ramp to energize the electro-hydraulic control valves that control the actuation of transmission clutch packs in a reverser transmission. By ramping up the hydraulic pressure slowly, in response to the slow current ramps, acceleration is non-aggressive.
With the switch in the more aggressive position, the current ramps and resultant pressure ramps are faster, thus causing more aggressive transmission operation for the reverser transmissions.
The two-position set switch could be replaced with a potentiometer, thus permitting an infinitely variable range in transmission aggressiveness control.
By providing the tractor operator with selectable transmission aggressiveness, the operator can choose the acceleration/deceleration rates according to the operator""s comfort or skill level and/or to the task being performed. The vehicle performance, controllability and productivity will be improved.
The invention also provides an interlock system. The system is used for a reverser transmission to prevent unanticipated motion. In order to start the engine on the tractor, the following must be sensed at the controller:
1. The forward-neutral-reverse lever must be sensed by the controller to be in neutral. Neutral is defined as having a neutral signal in combination with no forward signal and no reverse signal.
2. The main transmission shift lever must be in neutral.
3. The tractor power-take-off must be turned off.
When the forward-neutral-reverse lever is in the neutral position, no clutch-actuating hydraulic pressure must be sensed in either clutch pack or the tractor engine will be shut off. When the forward-neutral-reverse lever is in forward, then clutch-actuating hydraulic pressure must be present in the forward clutch pack, but not in the reverse clutch pack or the engine will be shut off. Reverse drive also has similar logic. Because clutch pack hydraulic pressures will be in transition when the forward-neutral-reverse lever is moved from one position to the other, time delays are provided to permit the ramping up or ramping down of pressure signals before the interlock logic is applied.
If hydraulic pressures in the forward or reverse clutch packs are not realized in approximately one second after the respective signal is received from the forward-neutral-reverse lever, then the controller will disable motion in that direction until another neutral signal from the forward-neutral-reverse lever is sensed.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.